Implantable medical device with lead failure detection

ABSTRACT

An implantable heart stimulating device has an ECG sensing unit to receive heart potential signals from sensing electrodes at an electrode lead arranged in connection with a patient&#39;s heart. The ECG sensing unit is provided with a programmable make-break threshold. The device further has a timer adapted to generate a make-break detection period, and a counter. The counter is adapted to count the number of times that the amplitude of the heart potential signal exceeds the programmable make-break threshold during the make-break detection period. When the number of times is higher than a predetermined value, the ECG obtained during the make-break detection period is stored in an ECG storage unit.

FIELD OF THE INVENTION

The present invention relates to an implantable heart stimulating deviceaccording to the preamble of the independent claim, and in particular toan implantable heart stimulating device, being a pacemaker,defibrillator or cardioverter, provided with electrode leads havingstimulation surfaces adapted to apply stimulation energy to hearttissue.

BACKGROUND OF THE INVENTION

An early indication of lead insulation defects, broken/damaged leadconductors and loose set screws/improper lead connection may be providedby the intermittent occurrence of so-called make-break signals, whichthen may remain unrecognized for a longer period of time. Even extensivefollow-up evaluation of a sporadic symptomatic patient often fails todisclose indications of an imminent lead or lead connector failure,since the make-break signals might only be prevailing in a certain,specific body position.

Make-break signals may arise when:

-   -   The lead conductors make intermittent contact with each other        due to an inner lead insulation defect/damage.    -   The outer conductor makes intermittent contact with the pulse        generator housing due to an outer insulation defect/damage        (caused by the lead insulation being rubbed off against the        pulse generator housing).    -   The outer conductor makes intermittent contact with the outer        conductor of another lead due to the fact that the leads have        crossed each others in the pulse/ICD pocket and rubbed off each        others insulations.    -   The two ends of a broken lead conductor meet intermittently.    -   A loose set screw.    -   A lead connector pin not fully inserted into the pulse generator        connector.    -   The electrode(s) or outer insulation defects touches the        electrodes of another lead inside the heart.

Make-break signals may cause:

-   -   Inhibition/triggering of pacemaker stimulation.    -   Noise mode reversion with risk for T-wave stimulation.    -   Triggering of inappropriate ICD therapy.

It is realistic to assume, that lead insulation/conductor damages aswell as connector problems in pacemaker/ICD systems will continue tooccur to some extent also in the future. According to clinicalexperience incipient lead and/or connector failures are often difficultto disclose at an early stage.

Thus, the development of life threatening conditions in some patientsmay remain unrecognized for substantial periods of time despite normalfollow-up intervals. However, early disclosure of lead and connectionfailures is of outmost importance for patient safety and would benefitfrom new, preferably automatic, diagnostic approaches.

U.S. Pat. No. 5,558,098 relates to a method and apparatus for detectinglead sensing artefacts in cardiac electrograms, the sensing artefactsare caused by lead conductor fracture, lead insulation failure orconnector port fluid penetration. The system includes at least two pairsof sensing electrodes which provide two distinct electrogram signals tothe sensing and analysis circuitry of a pulse generator. Each signal isanalyzed for heart rate. The rates are compared and if the ratesdetected are significantly different therapy is not delivered to thepatient. In an alternative embodiment, the two signals are compared byperforming a correlation analysis.

In this known device a comparison between two distinct electrogramsignals from at least two pairs of sensing electrodes is performed inorder to obtain an indication of e.g. a lead conductor fracture.

A drawback of this known device is that extra hardware is required, e.g.in the form of extra sensing electrodes and means for connecting theelectrodes to the measurement means, in order to perform themeasurement.

The object of the present invention is to achieve an implantable heartstimulating device, provided with means to detect e.g. lead connectorfractures or damages, that is easily implemented into a heartstimulating device and that not requires extra hardware.

SUMMARY OF THE INVENTION

The above-mentioned object is achieved by the present inventionaccording to the independent claim.

Preferred embodiments are set forth in the dependent claims.

According to the present invention an implantable heart stimulatingdevice comprising ECG sensing means to receive heart potential signalsfrom sensing electrodes at an electrode lead arranged in connection witha patient's heart. The ECG sensing means has a programmable make-breakthreshold, and the device further comprises a timing means generating amake-break detection period, and a counting means, wherein the countingmeans is adapted to count the number of times that the amplitude of theheart potential signal exceeds the programmable make-break thresholdduring the make-break detection period, and when the number of times ishigher than a predetermined value, the ECG obtained during themake-break detection period is stored in an ECG storage means.

The stored ECG signal may then be further analysed in order to determineif the indication of a lead defect is valid. This occasional occurrenceof make-break signals could e.g. be disclosed at routine follow-ups byretrieving the internal device memory.

Thus, by initiating storing of electrocardiograms (including sensedevent registration) in the presence of intermittent male-break signalsearly disclosure of impending lead/connection failures could herebybecome established, well before progress into life-threateningconditions.

No extra hardware is required to implement the invention as all modernpacemakers and ICD:s are able to store electrocardiograms intended toreveal a variety of preset rhythm anomalies, and includes programmingcapabilities to implement the timing and counting means.

Generally, the present invention provides a new triggering event forstoring ECG-segments to be further analysed.

SHORT DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 shows a schematic block diagram illustrating the heartstimulating device according to the present invention.

FIG. 2 shows the present invention implemented on an ECG signal.

FIG. 3 is a flow diagram illustrating the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic block diagram illustrating the heartstimulating device according to the present invention.

In FIG. 1 is illustrated the implantable heart stimulating devicecomprising an ECG sensing means 4 adapted to receive heart potentialsignals 2 from sensing electrodes (not shown) arranged in connectionwith a patient's heart. The sensing means includes amplifier means,filtering means and other signal processing means, which all arecommonly used in implantable heart stimulating devices and therefore notfurther discussed herein. The ECG sensing means is provided with aprogrammable make-break threshold. The stimulating device furthercomprises a timing means 14 adapted to generate a make-break detectionperiod 12, and a counting means 10. The counting means is adapted tocount the number of times that the amplitude, preferably the absoluteamplitude, of the heart potential signal exceeds the programmablemake-break threshold during the make-break detection period. When saidnumber of times is higher than a predetermined value, the ECG obtainedduring the make-break detection period is stored in an ECG storage means16. Preferably, the predetermined value is 3, 4 or 5, but any highervalue may also be used.

The counting means and the timing means is preferably implemented insoftware. According to a preferred embodiment the make-break detectionperiod is initiated when, and in parallel to, a refractory period, usedin connection with normal heart stimulation procedures, is initiated.The make-break detection period may also be initiated by a prematureventricular contraction (PVC) or by another predefined intrinsic orstimulated heart event.

According to another preferred embodiment the make-break detectionperiod has a programmable length being a programmable percentage,between 20-100%, of the length of the escape interval used in connectionwith normal heart stimulation procedures. If the detection period has alength of 100% of the escape interval the make-break signal detection isconstantly activated, i.e. it enables detection of make-break signalsduring the entire heart cycle.

The counting means is reset after each heart cycle.

The stored ECG may be analysed, either by analysing means (not shown)integrated in the medical device or in an external analysing means in anexternal programming device (not shown), a “programmer”, in order todetect defects or damages of the electrode leads and/or electrodeconnections. Preferably, the programmer, when initiated a communicationsession with the implantable device, directly alerts the physician thata lead failure has been indicated.

In addition, the implantable device may be provided with a patientnotifying means (not shown) adapted to notify the patient in case ofdetected anomalies. The notifying may be achieved by sound or by agenerated vibration.

FIG. 2 shows the present invention implemented on an ECG signal. In thefigure four heart cycles are shown by schematically illustratedQRS-complexes, either intrinsically initiated or stimulated by the heartstimulating device. In this case make-break detection periods areinitiated when the QRS-complexes occur.

In the figure make-break signals occur in the third heart cycle and inthis specific example the absolute ECG signal exceed the make-breakthreshold at least nine times during the make-break detection period andif the predetermined value is e.g. four, the ECG signal during the thirdheart cycle will be stored.

FIG. 3 is a flow diagram schematically illustrating the presentinvention.

In the first box of the flow diagram the (absolute) ECG amplitude of theECG-signal is compared to the programmable make-break threshold and ifthe amplitude is greater than the threshold it is determined, in thesecond box, whether the ECG-signal is measured within the make-breakdetection period. If within the period the count performed by thecounting means is increased. If not within the detection period and thedetection period has ended it is checked if the number of count isgreater than a predetermined value. If it is not greater, the countingmeans is reset and the procedure returns to the first box for ECGamplitude measurement. If the number of counts during the detectionperiod is greater than the predetermined value the ECG signal during thepresent heart cycle is stored in the storage means, for furtheranalysis, and the counting means is reset.

If it is determined as a result of the analysis that the electrode leadis damaged the physician has to decide if the electrode lead should bereplaced or if any other procedures should be undertaken, e.g.reprogramming of the pacemaker.

The present invention may naturally also be used to store ECG-signalshaving the erratic nature of a make-break signal, but not caused by e.g.an electrode damage, but instead caused by any heart event, e.g. R on Tphenomenon or retrograde P-waves, for later analysis.

The present invention is not limited to the above-described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

1.-8. (canceled)
 9. An implantable heart stimulating device comprising:an electrode lead configured for in vivo implantation in a patient, saidelectrode lead carrying at least one sensing electrode configured tointeract with the heart of the patient when the electrode lead isimplanted in the patient; an ECG sensing unit that receives cardiacpotential signals from said electrode; said ECG sensing unit beingprovided with a make-break threshold indicative of a level of saidcardiac potential signal associated with proper functioning of saidelectrode lead and said electrode; a timer that generates a make-breakdetection period; a counter that generates a count representing a numberof times that said cardiac potential signals exceeds said make-breakthreshold; and a storage unit connected to said counter and to said ECGsensing unit, said counter being configured to cause transfer of the ECGsignal obtained during said make-break detection period to said storageunit if said count in said make-break detection period exceeds apredetermined value.
 10. An implantable heart stimulating device asclaimed in claim 9 comprising heart stimulating circuitry that operateswith a refractory period, and wherein said timer is connected to saidheart stimulating circuitry and is configured to start said make-breakdetection period coinciding with a start of said refractory period. 11.An implantable heart stimulating device as claimed in claim 9 comprisingheart stimulating circuitry that operates with a refractory period, andwherein said timer is configured to generate said make-break detectionperiod in coordination with multiple refractory periods.
 12. Animplantable heart stimulating device as claimed in claim 9 comprisingheart stimulating circuitry that operates with an escape interval, andwherein said timer is configured to generate said make-break detectionperiod with a programmable length that is a percentage between 20% and100% of a length of said escape interval.
 13. An implantable heartstimulating device as claimed in claim 9 wherein said ECG sensing unitidentifies a beginning of each heart cycle of said heart, and whereinECG sensing unit resets said counter after each heart cycle.
 14. Animplantable heart stimulating device as claimed in claim 9 comprising ananalysis unit that analyzes the ECG signal stored in said storage unitto identify specific defects or damages of said electrode lead orinteraction of said electrode with the heart of the patient.
 15. Animplantable heart stimulating device as claimed in claim 14 comprisingan alarm generator that emits a humanly perceptible alarm if saidanalysis unit identifies a defect or damage associated with saidelectrode lead or said electrode.
 16. A medical system comprising: animplantable heart stimulating device comprising an electrode leadconfigured for in vivo implantation in a patient, said electrode leadcarrying at least one sensing electrode configured to interact with theheart of the patient when the electrode lead is implanted in thepatient, an ECG sensing unit that receives cardiac potential signalsfrom said electrode, said ECG sensing unit being provided with amake-break threshold indicative of a level of said cardiac potentialsignal associated with proper functioning of said electrode lead andsaid electrode, a timer that generates a make-break detection period, acounter that generates a count representing a number of times that saidcardiac potential signals exceeds said make-break threshold, and astorage unit connected to said counter and to said ECG sensing unit,said counter being configured to cause transfer of the ECG signalobtained during said make-break detection period to said storage unit ifsaid count in said make-break detection period exceeds a predeterminedvalue; an extracorporeal programming device; communication unitsrespectively contained in said implantable heart stimulating device andsaid programming device allowing said programming device to access theECG signal stored in said storage unit; and said programming unitcomprising an analysis unit configured to analyze the ECG signal storedin said storage unit and communicated to said programming device toidentify defect or damages of said electrode lead or interaction of saidelectrode with said heart.